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Tuning Diana 48 issue

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Danoh

Member
Jan 17, 2022
275
115
Ohio, United States
Hello everyone, new guy (new to air guns also) here looking for expert advice.

I just today received a (well)-used 48 in .177, bought sight unseen, except for cell phone pics.

I put a cheap scope on and tried it out in my basement today and am chronying around 850 fps with 7.9 grn CPs. Also, after maybe 20 shots or so , the side lever became hard to cock - it would go about half it's travel, then feel like it's catching on something. A couple times I had to let lever all the way back to start.

Every cocking cycle now, it's like I'm hitting a rough spot. I did take the rifle out of the stock and there is nothing obvious to me.

I'm sorta thinking perhaps a broken spring?

Any advice greatly appreciated.
 
Probably a broken spring. The factory springs, particularly in the older ones, were fairly brittle and tended to break. 

A new spring and seal from Air Rifle Headquarters should have it going again and will last a very long time. It will shoot better than it ever has. 

I have used this kit in a Mod48 in .22 and it was an excellent shooter. Slightly below "wide open" power, but the gun will shoot very pleasant and still make plenty of power. In .177 it would definitely be my first choice. 

https://www.airrifleheadquarters.com/catalog/item/251488/6962763.htm

And a new piston seal: https://www.airrifleheadquarters.com/catalog/item/251485/43075.htm

And breech seal: https://www.airrifleheadquarters.com/catalog/item/251485/10228725.htm

If you take it apart, the moly paste from there is what you will need to lubricate the insides properly: https://www.airrifleheadquarters.com/catalog/item/251484/42989.htm

A proper rebuild will have the gun shooting well for many years of heavy use. It's certainly worth the investment IMO. 


 
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Thanks for the quick reply! I’m new to airguns, but have been reading a LOT and this seemed the most likely answer. 
Well, I guess I need to learn how to tear into one now. 
Thanks for the link.
Click to expand...

You're welcome!

One other thing, be careful not to ever force the lever closed. And if you take it apart be sure and adjust the latch link rod (connects the lever to the silver compression chamber) so that it's not too tight. You probably won't have to, but sometimes a new thick breech seal may make it a little too tight. When the lever is closed, that rod is designed to "bow" a bit under tension and if it's too tight it may break. And last time I ordered parts from RWS/Diana/Umarex it was a bit of a fiasco. As long as it isn't overstressed it will never be a problem. Unlikely that you will have ANY issue with it, but just mentioning it as a heads up.
 
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I appreciate the information, thank you. 
Right now there is zero tension on closing, you’re saying it should have a little?
Click to expand...

There should be a little, yes. The breech seal is probably smashed out flat from being old. Look at it and it's probably smooshed looking. A new one will take a little "squish" to close and seal up well. 
 
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Would something like this suffice as a spring compressor? Worried it may flex too much in center. 
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555F2946-6095-49AA-9CDC-07BF1EFCCE84.1645117085.png

 
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That clamp will work on a rifle with not much preload. I tried a similar one on my 1970's FWB124 with Beau-Coup preload, and it was a struggle, because when loosening the handle, and walking the spring out, the handle runs out of threads and bottoms out while theres still some spring tension on it. If the handle has like 6" or more screw/throw, Id say get it. The one I have has like 3". It did work fine on my other FWB124 that has a Maccari kit in it, since theres not much preload. I found the "scissors-Car Jack" method works great, if you have a good work bench. Lots of throw and very controllable. Believe there a few Youtube videos on that method. Just my experience.
 
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That's kinda strange on the spring guide. Haven't seen one break there before.

Yes the breech seal goes in "flat side towards the piston" and the cupped face towards the barrel. 

That piston seal does look fine. I'd see how it fits. If it fits in the compression tube with very little resistance, I'd replace with it a new one and size it to fit properly. But if yours fits well with a slight snugness, rock on. You just want to make sure its sealing well for good consistency and good power. 
 
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